For many years minimum food safety processing standards for various commodities have been promulgated and enforced by the United State Department of Agriculture. While long enforced for liquid whole eggs and egg products of a wide variety, based upon minimum standards of pasteurization processing, food safety standards have never been established for shell eggs. Indeed, as a review of the prior art identified in this specification has shown, there has not heretofore even been available technology for successfully pasteurizing shell eggs to acceptable standards, that is, to standards equaling USDA guide-lines established for the other egg products mentioned above.
Shell eggs are an important commodity affording the consumer many nutritional advantages unparalleled by any other food product. These advantages include very favorable costs per nutritional unit of food value, convenience of preparation, gastronomic enjoyability, culinary usefulness, and availability.
It has long been known that some shell eggs contain infectious organisms such as Salmonella which, from a food safety standpoint, is of primary concern. Techniques for improving the food safety of shell eggs by destroying these infectious microorganisms have been proposed. However, aside from those effective for external sanitation, none are known to have ever been successfully employed. Instead, processing, handling, and other aspects of egg production have been emphasized in an effort to indirectly reduce the magnitude of the problem.
Awareness and concerns regarding infectious organisms in the yolk of a shell egg have been slow in developing. Both awareness and concerns have been amplified increasingly over the past decade as a result of numerous outbreaks of food poisoning irrefutably attributable to such yolk-associated organisms.
Advanced social programs and medical care have made a vastly enlarged percentage of the population dramatically more vulnerable to toxic effects of such food borne infections. At increased peril are those significant segments of the population of increased longevity or those who are immunocompromised due to organ transplants, immunosuppression therapies, and diseases caused by or causing compromised immune systems such as AIDS.
Increasingly, concerns over the safety of eggs consumed as a food illuminate the issue of transovarian infection developed deep inside the egg as it is formed in the oviduct. In addition, infectious organisms are known to penetrate the pores of shells and perhaps even the vitelline membranes of eggs, contaminating deeper proteins including the yolks. Also, for reasons not entirely clear, diseased hens are now known to excrete microorganisms inside the egg. The offending microorganism currently identified with this problem is Salmonella enteritis (S. enteritis).
Salmonella are small, gram negative, non-sporing rods. They are indistinguishable from Escheichia coli (E. coli) under the microscope or on ordinary nutrient media. All species and strains are currently presumed to be pathogenic for man.
As a disease organism, Salmonella produces a variety of illnesses depending on the species. S. typhimurium, which translates to "Salmonella from Typhus Mary", needs no other explanation. S. typhi causes enteric fever. S. paratyphi type A and type B cause a syndrome which is similar to but milder than typhus.
Reported cases of severe gastroenteritis (stomach flu) have implicated S. bareilly, S. newport, and S. pullorum as well. The mortality range is primarily based on the victim's age and general health. S. choleraesuis has the highest reported mortality rate at 21%.
S. senftenberg is reputedly the most heat resistant specie of Salmonella. It is reportedly destroyed at 130.degree. F. (54.4 .degree.C.) after 2.5 minutes. It is estimated that S. senftenberg 775W is 30 times more heat resistant than S. typhimurium. Turkeys (10 to 11 lbs.) inoculated with 115,000,000 microorganisms of S. pullorum required holding at an average internal temperature of 160.degree. F. (71.1.degree. C.) for four hours and 55 minutes before the bacteria were destroyed.
Over 2,000 other species of Salmonella are known. The number increases yearly.
Among the most common vehicles for food poisoning caused by Salmonella are eggs. Widespread publicity on illnesses and deaths attributed to contaminated eggs containing S. enteritis in Europe over the past few years has reportedly resulted in a reduction in egg consumption. In some distinct marketing areas the reduction has been estimated to be as great as 50 percent. The problem is being perceived in Europe and in the United States as chronic, spreading, and a major public health challenge. Nevertheless, in the United States alone, approximately 240,000,000 dozen eggs are still consumed annually.
A recent article in the Nutrition Action Health Letter published by the Center for Science in the Public Interest (July/August 1991 edition, Volume 18, number 6, "NAME YOUR (FOOD) POISON") relates a current trend of growing concern. The article reports that, according to government estimates, 80,000,000 cases of food poisoning yearly result in about 9,000 deaths and several billions of dollars in health costs.
The article claims that the primary causative foods are, in order: dairy products, eggs, poultry, red meat, and seafood.
The article reports that 1 in 10,000 eggs is contaminated with Salmonella enteritis. The average American consumes about 200 eggs per year. If your egg consumption is average, your chance of downing an egg contaminated with one or more species of Salmonella is 1 in 50; or, put another way, it is likely that you will eat four contaminated eggs this year.
If you are over 65 or have a disease such as cancer or AIDS associated with a weakened immune system, the article advises: don't eat raw eggs; don't drink egg nog; don't eat Caesar salads, home made mayonnaise, ice cream, or "health" drinks that call for raw eggs. Cook all eggs thoroughly--solid white and yolk.
Compounding the contamination problem is the improper handling of eggs in institutional and even home settings. Often cited is the all too frequent observation of eggs setting out at room temperature for long periods of time in institutional kitchens. Such unknowledgeable treatment promotes bacterial advancement in even the freshest egg.
Little is known about virology inside the egg. It has long been and is still believed by some that shell eggs are sterile inside the shell. Needle puncture samples of the inside of an egg including both yolk and white taken under aseptic conditions usually do demonstrate a negative plate count when cultured. Nevertheless, it is well known that, when eggs are broken in quantity, they immediately demonstrate significant gross populations of infectious microorganisms. It is not unusual to find plate counts ranging from several hundred to many thousands, even when the surface of the egg shells have been cleaned of filth and washed in the best antiseptics known to food science. The occurrence of S. enteritis inside the shell egg is now also well documented.
One source of infection arises from the fact that egg shells have numerous pores which permit the egg to breathe. Pore holes vary in size. When the egg is laid, those holes come into contact with organic refuse in the cage. It is very likely that some microbes contacting the egg are of a size which allows them to fit through the pores. Once inside, the microbes are not uniformly spread around the interior of the egg but are retained in small patches on the inner shell membrane, which has yet smaller pores than the shell.
Washing actually spreads microbes more evenly, increasing contamination through greater surface contact with entry pores in the egg shell. When the eggs are cracked, the shell membranes may be ripped and torn loose. And, when the shells are subsequently emptied, the eggs may be peppered with this stored inoculum in addition to airborne bacteria.
Also, as egg temperatures vary, there is active and ongoing gas and vapor exchange between the yolk and white via the vitelline membrane, between the white and the inside of the shell via the outer and inner shell membranes, and also between the shell and the outside environment. Airborne microorganisms can also reach the interior of the egg through these mechanisms.
Finally, as discussed above, eggs can be, and frequently are, contaminated by transovarian infection. The extent of this problem is still not known. Thus, an egg may be unsafe to eat even if there is no transport of harmful microorganisms from the exterior of the egg to its interior. Worse yet is when both of the egg infecting mechanisms--pore penetration and transovarian infection--are at work.
U.S. Pat. No. 4,808,425 issued Feb. 28, 1989 to Swartzel et al. elaborates on the USDA stanards for pasteurizing liquid eggs, summarizes the disclosures of many references, identifies resources relative to egg pasteurization, and adequately points out many of the problems associated with available techniques for making liquid but not shell eggs of safer food quality. Swartzel et al. employ a conventional pasteurization technique--time at temperature--to treat liquid egg products. The products are contacted against a heated surface at high temperatures; i.e., above 140.degree. F. (60.degree. C.) for short durations of less than 10 minutes. This approach is not applicable to a shell egg.
The minimum time at temperature processing mandated by USDA standards produces liquid eggs which are safe to eat because all particles have been exposed to RPT; and, if the liquid eggs are carefully processed, an at least acceptable degree of functionality and other valued properties can be retained. Standards for shell eggs are lacking because, up to now, a reliable time at temperature technique for making shell eggs safe to eat has not existed. In particular, there is not known to exist any effective process which can be employed to process whole eggs to the standards mandated for liquid eggs; i.e., to ensure that all particles throughout the mass of the egg--which includes the shell, the outer shell and egg membranes, the albumen layers or egg white, the chalaza, the vitelline membrane, and the yolk to its innermost reaches or center--are exposed to appropriate temperatures for times adequate for an acceptable kill of any harmful organisms that might be present.
Other researchers have focused their attention on time and temperature treatments for devitalization of vital shell eggs. To a much lesser extent, pasteurization of shell eggs to improve food safety quality has been considered.
Funk (Stabilizing Quality in Shell Eggs, Missouri Agricultural Experimental Station, Research Bulletin no. 362 and Maintenance of Quality in Shell Eggs by Thermostabilization, Missouri Agricultural Experimental Station, Bulletin no. 467) and Murphy and Sutton (Pasteurization of Shell Eggs to Prevent Storage Rot and Maintain Quality--a Progress Report of Experimental Work, Misc. Publication no. 3317, Department of Agriculture, New South Wales, Australia) purported to preserve shell eggs by briefly heating the eggs for 15 or 16 minutes at temperatures ranging from 130 to 135.9.degree. F. (54.4.degree. C. to 57.7.degree. C.) and from 129.2 to 136.4.degree. F. (54.degree. C. to 58.degree. C.). Irrespective of the starting temperature of the shell egg to be processed, these prior art processes cannot possibly provide a Salmonella free or Salmonella reduced inner egg. Neither can they achieve equivalents of the minimum requirements established by the USDA for processing liquid whole eggs.
The growth of external food poisoning infections are in some of the TPT/temperature ranges provided favorably influenced in the outermost layers of the shell egg. In many other ranges, external food poisoning infections will be significantly worsened. In all cases, temperatures near and at the egg yolk center never achieve the minimum temperature needed for a time effective to kill significant concentrations of infectious microorganisms.
On the contrary, because the internal temperatures reached near or in the center of the yolk are not high enough to destroy Salmonella and other infectious microorganisms, these prior art techniques, irrespective of how employed or combined, cannot meet accepted minimum standards for other egg products and by and large can only attain temperatures in the yolk within the times suggested which are in a range that will cause substantial increases of any food poisoning infections present therein. Within a very narrow range of those parameters, processed eggs may or may not become more infected. In all other instances a shell egg carrying a minor, non-lethal infection in the yolk can by use of such methods deteriorate markedly and become a very significant health risk, if not a toxic food.
In his U.S. Pat. No. 2,423,23 issued 1 Jul. 1947, Funk is concerned principally with "sterilizing or devitalizing" embryos in vital shell eggs. Confusingly, Funk ambiguously and interchangeably uses the term sterilization, stabilization, devitalization, and pasteurization in describing this objective. Funk claims that poultry eggs can be pasteurized, stabilized, and devitalized of embryonic life by immersing freshly laid, room temperature eggs in oil or water at temperatures ranging from 110.degree. F. to 145.degree. F. (43.3.degree. C. to 62.8.degree. C.) for times ranging from five to forty minutes or presumably, in the alternative, from 110.degree. F. to 145.degree. F. for from forty to five minutes.
Funk did not account for the fact that infectious microorganisms such as Salmonella are to be found throughout and in any or all specific parts of an egg, such as the yolk, whites, and membranes and even at the center of the yolk. Funk is principally concerned with devitiating the shell egg embryo and only with "destroying bacteriological organisms which may have penetrated the egg shell and . . . extended even so far as the yolk . . . . " He did not disclose in his patent or take into account the fact that the time required for processing a shell egg to make it safe to eat at specified temperatures is one thing for the outer, non-yolk portion of a shell egg and quite another for the center of the yolk. The result is that most of the process conditions claimed by Funk only result in conditions which at best can not meaningfully improve any preexisting infectious condition and at worst are certain to significantly increase health hazards from food poisoning infections. As applied to a shell egg, Funk cannot achieve even the minimum USDA processing standards (see FIG. 2) for liquid egg products. Use of other time/temperature combinations embraced by the broad statements in the Funk patent (which also cannot meet the minimum processing standards referred to above) result in the whites of the eggs being visibly cooked (see FIG. 8).
The Funk process parameters are temperature and TPT. As defined above, this is the total time a shell egg is held in a pasteurization medium heated to a selected pasteurization process temperature. This is quite different from the critical RPT, which is that portion of TPT in which all particles throughout the mass of the egg including those at the center of the yolk are at an effective pasteurization temperature measured from the point at which EqT is reached. There is no evidence that Funk recognized or appreciated the criticality of the difference between TPT and RPT. Even if he had, he presumably would not have made this distinction because, for purposes of devitiating an egg embryo, TPT and RPT are one and the same; i.e., there is little or no difference between these two process temperature conditions in pasteurizing, devitalizing, and sterilizing whole eggs to retard spoilage by making viable eggs infertile; i.e., by preventing ongoing embryonic development.
Lethal thermal damage to any part of an embryo, even only at its surface, is adequate for this purpose. Unlike the embryos in vital eggs, infections are composed of a multitude of micro-entities. Lethal damage at some point to a portion of this multifarious milieu is not adequate to destroy the infection as is the case with an embryo which may be killed if even a small part is heated to a high enough temperature. To be effective against infections frequently scattered throughout a substrate, the time at temperature must be adequate to kill large numbers of infectious organisms at these widely scattered locations. In a shell egg, that means that the pasteurization temperature must be reached and maintained for the necessary time throughout all parts of the egg containing the microorganisms. In this case, TPT and RPT are distinct; the distinction becomes increasingly critical as that mass of the egg which is potentially infectable is increased.
Funk's statement of process parameters for the devitalization of an egg embraces many time and temperature combinations which may be effective to achieve that object. However, when employed to kill food borne infections, those time and temperature combinations which apply to embryonic devitiation cannot adequately kill Salmonella or other harmful bacteria commonly found in eggs for reasons just discussed. The unfortunate fact is that most of those time/temperature combinations embraced in Funk can only significantly increase contamination inside the egg because they for the most part result in the egg being under conditions near to or optimal for maximum bacterial growth. An example is Funk's own preferred pasteurization parameters--five to ten minutes TPT at 138.degree. F. (58.8.degree. C.) and twenty to forty minutes TPT at 130.degree. F. (54.4.degree. C.).
Funk's preferred "pasteurization" method for a shell egg never achieves any RPT at the yolk but does achieve active growth range conditions there over a significant period of time. If the initial temperature of the shell egg is significantly lower than 70.degree. F., as is or should always be the case in real world processing, Funk's preferred conditions will more seriously fail, resulting in dramatically favored conditions likely to increase any food poisoning infection present in the yolk.
Funk's preferred "pasteurization" process times and temperatures are not the worst cases suggested to one of ordinary skill in the art by his patent. Indeed, when many, if not most, of the Funk times and temperatures provided for pasteurization, sterilization, and devitalization of vital egg embryos are applied to the "pasteurization" of shell eggs to improve food safety quality, the results as confirmed by tests always fall short of and are often contrary to that objective. Moreover, as measured at the yolk, eggs processed pursuant to the most favorable possible conditions specified by Funk cannot meet the process standards provided in the USDA Protracted Whole Egg Standard for Liquid Whole Eggs (see FIG. 1) or even the minimum standards mandated by the USDA for liquid whole eggs (see FIG. 2).
For example, take a shell egg infected superficially at the inner shell surface (not uncommon) and also in the yolk (estimated to occur in 1 out of every 10,000 eggs). Pasteurize that egg according to Funk's specifications: from 40 minutes at 110.degree. F. to 5 minutes at 140.degree. F. At the lower temperature/longer time--40 minutes at 110.degree. F.--the superficial temperatures even at the inner surface of the shell can be expected to promote the growth of bacteria and result in substantial worsening of any food poisoning infections present. Those temperatures achieved near or at the yolk center could reach but would never exceed the optimal growth conditions for food poisoning infections of Salmonella. The result, if infections were present, could easily be catastrophic increases in food poisoning concentrations. At shorter times and higher temperatures such as 134-136.degree. F., the temperature of an infected yolk center would never exceed about 125.degree. F., yielding only eggs with increased food poisoning potential.
If the above-discussed time/temperature relationships are reversed--5 minutes at 110.degree. F. to 40 minutes at 140.degree. F.--as is equally reasonable from Funk's claim 1 and other statements in his patent, the low temperature/short time relationships constitute what could reasonably be selected as optimal by a bacteriologist to best culture Salmonella in eggs as a growth medium. At the other end of the spectrum--the extreme high temperature/long time combination of 140.degree. F. for 40 minutes--, the "pasteurized" eggs would be "hard-boiled" in at least the exterior layers. All inbetween permutations of Funk conditions are ineffectual at best to meet even the minimum processing conditions required by the USDA for liquid whole eggs as shown in FIG. 2.
At the same time, even starting with shell eggs already at 70.degree. F., let alone at more realistic, lower, cold storage temperatures, shell eggs processed according to Funk in the near extreme regime (&gt;139.degree. F./39.2 to 40 minutes TPT) will never achieve the RPT near or at the egg center needed to meet the basic protracted USDA temperature/time regimes for liquid whole eggs. To make matters worse, when shell eggs are immediately immersed into liquid at extreme temperature differentials (greater than about 65.degree. F.-70.degree. F.) as they could well be in following Funk's teachings, a significant number will crack. Cracked eggs are a loss. They are difficult to handle, unmarketable to consumers and other purchasers of whole eggs, and exceptionally susceptible to contamination.
In short, by even the most generous interpretation, no obvious combination of Funk's sterilization, devitalization, or pasteurization temperatures and times (from 110.degree. F. to 140.degree. F. for 5 to 40 minutes or from 110.degree. F. to 140.degree. F. for 40 to 5 minutes) can achieve even the minimum, FIG. 2 USDA process standard for liquid whole eggs without "cooking" at least the egg whites to some extent; and this is unacceptable because of consumer rejection and resulting loss of functionality. It is more likely, because it is true in the large majority of the available time/temperature combinations, that the Funk process would, if the egg being processed is infected at the yolk and/or superficially on the shell's inner surface, increase rather than decrease, perhaps dramatically, any food poisoning hazard present. The process would surely promote the growth of or at best substantially leave unaffected any harmful microorganisms present in the egg.
Application of the Funk process to eggs almost certainly results in eggs dependably rid of a living embryo. But with respect to pasteurization designed to improve food safety of shell eggs and with the questionable exception of a few time and temperature combinations effective to reduce superficial inner shell infections, Funk's process is only likely to produce infected shell eggs which remain or are made more hazardous to consumers and/or which are visibly partially cooked at the outer layers.
New serotypes of infectious organisms continue to develop. Increased production, mass handling, and widespread distribution of food products continue to increase the risks of food poisoning. Food poisoning incidents related to eggs are not uncommon and may even be increasing. Almost all food products have well developed standards of processing for ensuring food safety. With respect to eggs and egg products, only shell eggs have no standards for pasteurization. The primary reason for this lack of food safety pasteurization standards as required for all other egg products is undoubtedly attributable to the lack of knowledge of an efficacious process for making shell eggs safer to eat. In practice, known processes such as the one discussed above and proposed by Funk are inefficacious and either fail completely to achieve any meaningful benefits or are highly likely if not certain to result in products with substantially increased health hazards from food poisoning.